CARLW. MOELLER, AKD ROLAND WARD 1572 ALANCALLAGHAN,
Inorganic Chemistry
COXTRIBUTIOS FROX THE CHEMISTRY DEPARTXENT, THEUSIVERSITYOF CONSECTICUT, STORRS, CONXECTICUT
Magnetic Interactions in Ternary Ruthenium Oxides BY ALAN CALLAGHAS, CARL W. MOELLER,
ANU
ROLASD WARD
Received M u y 27, 1966 The magnetic susceptibilities of six ternary ruthenium oxides in which the ruthenium atoms are in octahcdral coordination with oxygen have been measured from 77 to 1000'K. The perovskite-type SrIiuOa ( I ) is ferromagnetic ( T c = 160 rt 1O0K,t? = 161"K, pSat = 0.85 B M , high-temperature pefi = 2.6 BM). The isotypic CaRuOs (11),on the other hand, may be antiferromagnetic. The Weiss temperature is negative b u t the Nee1 point, if one exists, lies below the temperature range SrzRuO4 (111) (K2iYiF4structure) shows an almost constant paramagnetism over a covered ( p e f f = 3.0 B M , 0 = -119"). temperature range of 700'. BaRuO.: (IV), ( Bav6Sw8)Ru03(V),and Ba(Ruz&Igl:,)Oa (VI) all contain RuOe octahedra sharing faces. The first has strings of three octahedra sharing two faces connected by corner sharing of the outermost octahedra to adjacent strings; the second has two face-sharing octahedra connected to other pairs by corner sharing, while the third has two face-sharing octahedra connected by corner sharing through a MgO6 octahedron. The latter contains Ru(V). These three compounds all exhibit a low paramagnetism. The xm-T plots for IV and VI show broad maxima a t 430 and 390"K, respectively, whereas for 1' there is no maximum and only a slight temperature dependence. All of the substances are good conductors except VI. The magnetic behavior of IV,17, and VI is interpreted as evidence for metalmetal bonds between the ruthenium atoms in face-shared octahedra, and the data for VI agree well with Kambe's model for a spin-coupled binuclear system. SrRuOa appears to offer the first example of ferromagnetism attributable solely to a period 5 transition metal.
Introduction mostly pentavalent. Finally, we have SrzRuO,,jwhich does not conform to the close-packed layer type but has A simple relationship among the structures of a the K2NiF4structure in which the RuO6 octahedra lie large number of ternary oxides containing large cations in infinite layers sharing four equatorial oxygens. (A) can be found on the basis of the close-packing of This paper describes the determination of the magA03 1ayers.l Cubic or hexagonal stacking or alternanetic properties of all of these compounds. The tions of these layers result in 0 6 octahedra sharing results lend support to the concept of metal-metal corners or faces, respectively. The smaller cations, bonds in the compounds with hexagonal stacking which occupy all of these octahedra in compounds of sequences. the type AMOa, are thus brought together either by sharing one oxygen (corner sharing) or by sharing Experimental Section three oxygens (face sharing). The Madelung energies Magnetic Measurements.-Magnetic susceptibilities were of compounds with different structures of these types measured on an enclosed Gouy balance from 77 t o 1000'K. cannot be very different, and it has been proposed1n2 Low temperatures were obtained utilizing the slow warming of a mass of copper powder cooled in liquid nitrogen, and high temthat the hexagonal close-packing sequences result from peratures, by a small tubular furnace, noninductively wound. the formation of an &I-M bond sufficiently strong to A low-temperature calibration was performed using CuS04. overcome the increase in coulombic repulsion. 5HzO (xa = 5.92 X cgs unit at Z O O ) , and a plot of l / x m A series of ternary oxides of ruthenium provides us. T gave a straight line whose slope and intercept werc in an interesting sequence of structures in which RuO6 agreement with literature values. At low temperatures a presoctahedra are to be found in various j ~ x t a p o s i t i o n s . ~ ~sure ~ of 50 cm of dry helium was maintained in the balance case, and a t high temperatures, 10 cm was maintained. The susIn BaRuOa a nine-layer structure in which the sequence ceptibility of each sample was measured at three field strengths is hhc contains, along the c axis, strings of three faceat both room temperature and 77°K to test for ferromagnetic sharing Ru06 octahedra connected by corner sharing impurities, and the molar susceptibility of each sample was of the end octahedra (Figure l(i)). Partial substitution corrected for the underlying diamagnetism.e For SrRuOo, Sr2Ru04, and (Bas$,Sri,,)RuO~, several runs were performed on of the barium with strontium gives, a t composition two or more samples. For the other compounds two or morc (Bas,,Srli,)RuOs,a four-layer structure with stacking runs wcre performed on a single sample. The weight changes in sequence hc containing pairs of RUOFoctahedra conthe magnetic field were always in excess of 3 mg and could bc nected by corner sharing (Figure I($). In SrRuOs measured to i 0 . 0 2 mg, so the precision within a given run is and CaRuOa (perovskite structure) the RuOs octahedra Because of the errors considered to be better than il%. inherent in packing and calibration, the errors in the over-all share only corners, each oxygen being common to two susceptibility values are likely to be about 415%. rutheniums (Figure 1(iii)). Ba(Run,,Mgl,,)0 3 has the Preparation of Materials.-The preparation of these materials ordered hexagonal barium titanate (hcc) structure in has already been described by Randall6 (CaRuOa, SrRuOs, which pairs of face-sharing RuOG octahedra are conBa(Kun;,Mgii,)Oa, Sr2Ru04) and D ~ n o h u e ~(Bal;,Srl;,)RuOa, ,~ nected through corner sharing with MgOG octahedra and BaRuOa). They are all easily prepared by calcining appropriate mixtures of the alkaline earth carbonates or peroxides (Figure l(iv)). The ruthenium in this compound is (1) L, Katz and R. Ward, I m i g . C h e m . , 3, 205 (1964). (2) J. G. Dickinson, L. Katz, and I
